Structure, Bonding, and Stabilization Mechanism of High-Spin Cobalt- and Nickel-Based Metalized Borylene Complexes [(OC)BM(CO) _<i>n</i> ][M ₂ (CO) ₆ ] ⁺ (M = Ni, Co; <i>n</i> = 2, 3)

Borylenes (:BR) have garnered extensive interest in small-molecule activation due to their unique amphoteric reactivity, and thus, stabilizing these species remains of paramount importance for realizing their practical applications. Recently, metalized borylenes (:BM) have emerged as new variants of organoborylenes, although their stabilization mechanism remains incompletely understood. Herein, cationic cobalt- and nickel-based metalized borylenes were generated in the gas phase. Their saturated carbonyl complexes were structurally characterized by using infrared photodissociation spectroscopy (IRPD) and density functional theory (DFT) calculations, revealing high-spin electronic states and planar geometry with C_2v symmetry. The boron centers in these species exhibit pronounced σ-acidity and π-backdonation capabilities, with CO activation extents comparable to those of base-stabilized borylenes. Electronic structure and chemical bonding analyses elucidate the reciprocal stabilization mechanism between the unsaturated boron center and the surrounding metal atoms, confirming that constructing amphoteric metalized borylenes can extend beyond monovalent metals.